The invention relates to polyolefin fibers and polyolefin yarns, produced by melt processing and having high strength and elongation, particularly polyolefin fibers and yarns, which have not been afterstretched, and to textile fabrics produced therefrom.
Fibers, yarns and textile fabrics of polypropylene are known (U.S. Pat. No. 3,092,891; "Films, Woven and Nonwoven materials of Polypropylene", pages 175-189, VDI-Verlag, Dusseldorf, 1979; Moore, P., "Polypropylene-Handbook", pages 350-358, Carl-Hanser Verlag, Munich, 1996).
The methods of manufacturing fibers and yarns based on polypropylene differ depending on the spinning speed and on the aftertreatment of the spun fibers.
The high-speed spinning method and the abbreviated spinning method are known methods of manufacturing polypropylene staple fibers by melt spinning.
For the production of staple fibers based on polypropylene by the high-speed spinning method, already known as the high-speed spinning process for extruding polyester or polyamide filaments, the latter are drawn off at high speed (500 to 2000 m/min.) from the spinneret. Since the polypropylene macromolecules are not oriented completely by this method, the filaments produced must be drawn in a further step of the procedure. This is generally done in combination with other finishing steps.
The production of staple fibers based on polypropylene by the abbreviated spinning method is carried out at very low spinning speeds (30 to 150 m/min). As a result, the cooling zones of the spinning plants can be kept very short (Schweitzer, A., Chemiefasern/Textilindustrie 88 (1986), 671-674). The low spinning speeds enable the filaments, which are brought together to form tow, to be supplied directly and continuously to the drawing equipment and to the equipment further downstream.
The technology of high-speed spinning also results in POY (pre-oriented yarn) spinning, in which the filament, emerging from the spinneret, passes through the blast shaft of high-speed galettes or is drawn off directly by the winding machine at 1000 to 5000 m/min and wound onto cross-wound bobbins. The fiber properties are determined largely by the orientation introduced from the molten state (Wulfhorst, B., Chemiefasern/Textilindustrie 92 (1990), 971-976). This orientation effect results from the difference between the extrusion speed and the pull-off and winding speed.
Comparable relationships for effecting fiber properties exist also for the spunbonded nonwoven method. For the latter, the filaments are drawn off through the cooling zone either through accelerated downpipe air or through nozzles operated by compressed air (Fourne, F., Chemiefasern/Textilindustrie 95 (1993), 811-822). The undrawn filaments produced are deposited in two-dimensional disordered form on a screen-like conveyor belt and processed in a further step by the application of thermal bonding processes (by means of calender consolidation) or by needling processes into a spunbonded nonwoven material.
The melt-blow spinning technology, in which filaments are formed by the application of a heated stream of air about the openings of the capillary nozzle (Fourne, F., Chemiefasern/Textilindustrie 81 (1979), 445-449) represents a special variation of the nonwoven manufacturing process. The air stream divides the molten polymer filament into many small individual fibrils with a very small diameter and, at the same time, brings about a stretching of the individual filaments. The fibers or filaments, deposited on the screen conveyor belt, are processed further by the spunbonded nonwoven technology.
For the production of high strength filaments yarns (fully drawn yarn (FDY)), the filaments are drawn with the help of galettes from the spinneret and processed further in downstream equipment, comprising drawing equipment and winding machines. High strength filaments yarns can be produced by the abbreviated spinning method as well as the high-speed spinning method. In addition, for the bulked continuous filament method, drawing is accomplished by a three-dimensional crimping by texturing equipment (Bussmann, M., Chemiefasern/Textilindustrie 35 (1986) 87, 668-672).
The properties of the fibers, yarns and textile fabrics are determined by the manufacturing method and by the polypropylenes used.
The addition of nucleating agents leads to a lowering of the strength of the fibers (Richeson, G., ANTEC '96, 2305-2311). Formulations with fillers, such as calcium carbonate (Nago., S., J. Appl. Polymer Sci. 62 (1996), 81-86) or poly(methylsesquioxane) (Nago., S., J. Appl. Polymer Sci. 61 (1996), 2355-2359), after spinning and drawing, result in microporous fibers. Fibers of increased heat stability can be produced by spinning polypropylene blended polyethylene terephthalate (Qin, Y., J. Appl. Polymer Sci. 61 (1966), 1287-1292) or with liquid crystalline polymers (Qin, Y., Polymer 34 (1963), 3597).
Fibers of polypropylene have the disadvantage of a relatively low tensile elongation. The addition of elastomers, such as ethylene propylene rubber or ethylene propylene diene rubber leads to an increase in the elongation. At the same time, however, there is a great decrease in the strength of the polypropylene fibers and polypropylene yarns.